Self-Assembly of Discrete RuII₈Molecular Cages and Their in Vitro Anticancer Activity

Four new octanuclear Ru(II) cages ( OC-1 – OC-4 ) were synthesized from dinuclear p -cymene ruthenium(II) acceptors [Ru 2 (μ–η 4 -C 2 O 4 )(CH 3 OH) 2 (η 6 - p -cymene) 2 ](O 3 SCF 3 ) 2 ( A 1 ), [Ru 2 (μ–η 4 -C 6 H 2 O 4 )(CH 3 OH) 2 (η 6 - p -cymene) 2 ](O 3 SCF 3 ) 2 ( A 2 ), [Ru 2 (dhnq)(H 2 O) 2 (η 6 - p -cymene) 2 ](O 3 SCF 3 ) 2 ( A 3 ), and [Ru 2 (dhtq)(H 2 O) 2 (η 6 - p -cymene) 2 ](O 3 SCF 3 ) 2 ( A 4 ) separately with a tetradentate pyridyl ligand ( L 1 ) in methanol using coordination-driven self-assembly [ L 1 = N, N, N ′, N ′-tetra(pyridin-4-yl)benzene-1,4-diamine]. The octanuclear cages are fully characterized by various spectroscopic techniques including single-crystal X-ray diffraction analysis of OC-4 . The self-assembled cages show strong in vitro anticancer activity against human lung adenocarcinoma A549 and human cervical cancer HeLa cell lines as observed from the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Of all the octanuclear cages, OC-3 exhibits remarkable anticancer activity against both cancer cell lines and is more active than that reported for cisplatin. The excellent anticancer activity of OC-3 and OC-4 highlights the importance of the synergistic effects of the spacer component of the dinuclear p -cymene Ru(II) acceptor clips.